Method for modifying nickel microparticles and method for producing nickel microparticles

ABSTRACT

The purpose of the present invention is to provide a method for modifying nickel microparticles weight loss of which occurs due to heat treatment such as burning and a method for producing nickel microparticles comprising the modification method. 
     Provided is a method for modifying nickel microparticles comprising a step of making an acid and/or hydrogen peroxide act on nickel microparticles weight loss of which occurs due to heat treatment such as burning and a method for producing nickel microparticles comprising the modification method. The step of making an acid and/or hydrogen peroxide act reduces a rate of weight loss due to heat treatment of the nickel microparticles, nitric acid or a mixture of acids that include nitric acid is preferably used as the acid, and the nickel microparticles and acid and/or hydrogen peroxide are preferably made to act in a ketonic solvent.

TECHNICAL FIELD

The present invention relates to a method for modifying nickelmicroparticles and a method for producing nickel microparticles.

Nickel microparticles, which are a widely used material as anelectrically conductive material including a laminated ceramic condenserand a substrate thereof, as well as an electrode material, have beenused as ones controlled in crystallite diameter and particle diameterand particle size distribution according to purpose.

The methods for producing nickel microparticles include a method using agas phase method as known in Patent Document 1 and a method using aliquid phase method as known in Patent Document 2.

Generally, with nickel microparticles obtained using these methods, afew percent of weight loss is often confirmed in a simultaneous TG-DTA(Thermogravimetry-Differential Thermal Analysis) measurement, and whichcontributes to a defect such as cracking that occurs, for example,during burning when a laminated ceramic condenser is produced usingslurry of nickel microparticles for an internal electrode.

In addition, such nickel microparticles also have a problem in storagestability, and also often form nickel hydroxide in a few days to a fewweeks when stored under an air atmosphere, and there has been a problemsuch that use of nickel microparticles becomes difficult in that case.

The following conventional arts propose solutions to the above problems.For example, a method where hydrogen reduction processing using hydrogengas is performed after oxidizing nickel powder to some degree isproposed in Patent Document 3, and a method where nickel powder is addedinto and dispersed in an aqueous solution containing a water-solublefatty acid salt, the aqueous solution slurry is adjusted from acidic toneutral pH, the nickel powder is filtered out from the aqueous solutionslurry, the nickel powder thus obtained is heat-treated, then a solventslurry, prepared by mixing a solvent, a fatty acid, and the nickelpowder, is heated and stirred to volatilize the solvent, and thereafterthe nickel powder obtained is heat-treated is proposed in PatentDocument 4. A method where nickel microparticles having a nickelhydroxide coating are processed by a plasma of oxygen-containing gasgenerated by glow discharge to form a coating of nickel oxide isproposed in Patent Document 5.

However, the method of Patent Document 3 has such problems as requiringexplosion-proof measures for facilities and involving danger in theproduction of microparticles due to the use of hydrogen gas. Also, themethod of Patent Document 4 has such problems that the process becomesextremely complex, productivity is still low, it is difficult to removethe fatty acid salt absorbed to the nickel microparticle surfaces, andheat treatment is required. Further, with Patent Document 5, there aresuch problems as requiring high energy and an expensive apparatus forprocessing by the plasma of the oxygen-containing gas. Thus in regard tothe issues described above, the conventional arts not only havedifficulties in reducing the weight loss rate in the simultaneous TG-DTAmeasurement but also do not provide an industrially inexpensive simplesolution suited for mass production.

On the other hand, up to now, Applicant of the presently appliedinvention has proposed the methods for producing nickel microparticlesdescribed in Patent Document 6 and Patent Document 7. Patent Document 6relates to a method of separating nickel microparticles in a thin filmfluid formed between processing surfaces which are able to approach andseparate from each other and rotate relative to each other. In PatentDocument 7, there is described a method for making nickel microparticleshave a sharper particle diameter distribution, a method for controllingparticle diameter, and a method for controlling crystallite diameter. Bythe methods described in Patent Document 6 and Patent Document 7, it ispossible to mass-produce nickel microparticles of uniform particle sizedistribution extremely simply.

Even in terms of the nickel microparticles prepared using the productionmethods described in Patent Document 6 and Patent Document 7, however,there is no disclosure of a method for producing nickel microparticlesreduced in weight loss rate in simultaneous TG-DTA measurement, and thedefect such as cracking in the burning process cannot be solved when alaminated ceramic condenser is produced.

PRIOR ART DOCUMENTS Patent Document

-   Patent Document 1: Japanese Patent Laid-Open Publication No.    2014-189820-   Patent Document 2: Japanese Patent Laid-Open Publication No.    2014-162967-   Patent Document 3: Japanese Patent Laid-Open Publication No.    2001-073001-   Patent Document 4: Japanese Patent Laid-Open Publication No.    2003-129105-   Patent Document 5: Japanese Patent Laid-Open Publication No.    2014-173105-   Patent Document 6: Japanese Patent Laid-Open Publication No.    2009-082902-   Patent Document 7: Japanese Patent Laid-Open Publication No.    2014-023997

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

In light of such circumstances, the present invention provides a methodfor modifying nickel microparticles with a reduced weight loss rate insimultaneous TG-DTA measurement and a method for producing nickelmicroparticles comprising this method for modifying nickelmicroparticles.

As a result of an intensive examination carried out in order to solvethe abovementioned problems, the inventor of the presently appliedinvention have found that the abovementioned object can be achieved by amethod for modifying nickel microparticles to be described hereinafterand a method for producing nickel microparticles comprising this methodfor modifying nickel microparticles and thereby could accomplish thepresently applied invention.

Means for Solving the Problems

Specifically, the present invention relates to a method for modifyingnickel microparticles comprising a step of making an acid and/orhydrogen peroxide act on nickel microparticles weight loss of whichoccurs due to heat treatment such as burning.

The present invention relates to a method for modifying nickelmicroparticles, wherein the step of making an acid and/or hydrogenperoxide act reduces a rate of weight loss due to heat treatment of thenickel microparticles.

In addition, the present invention may be executed as an embodimentwherein the rate of weight loss due to heat treatment of the nickelmicroparticles is a weight loss rate in simultaneousthermogravimetry-differential thermal analysis measurement, and theweight loss rate in a simultaneous thermogravimetry-differential thermalanalysis measurement under a nitrogen atmosphere of the nickelmicroparticles is 1% or less in a range of 40° C. to 400° C.

Further, the present invention relates to a method for modifying nickelmicroparticles, wherein nitric acid or a mixture of acids that includenitric acid is used as the acid.

The present invention relates to a method for modifying nickelmicroparticles, wherein the nickel microparticles and acid and/orhydrogen peroxide are made to act in a ketonic solvent.

The present invention relates to a method for modifying nickelmicroparticles, wherein a molar ratio of the acid to the nickelmicroparticles is in a range of 0.001 to 0.1.

The present invention relates to a method for modifying nickelmicroparticles, wherein a molar ratio of the hydrogen peroxide to thenickel microparticles is in a range of 0.001 to 2.0.

The present invention relates to a method for modifying nickelmicroparticles, wherein the step of making an acid and/or hydrogenperoxide act includes an ultrasonic processing, a stirring processing,or a microwave processing.

In addition, the present invention may be executed as an embodimentwherein the stirring processing is performed using a stirrer providedwith a rotating stirring blade.

The present invention relates to a method for modifying nickelmicroparticles, wherein powder of the nickel microparticles on which theacid and/or hydrogen peroxide was made to act is stored under an airatmosphere.

The present invention relates to a method for modifying nickelmicroparticles, wherein the nickel microparticles are nickelmicroparticles separated by a microreactor which makes at least twokinds of fluids to be processed react.

The present invention relates to a method for modifying nickelmicroparticles comprising a step of making a substance which reacts withnickel hydroxide act on nickel microparticles on at least surfaces ofwhich nickel hydroxide is present to reduce the nickel hydroxide.

The present invention relates to a method for producing nickelmicroparticles comprising a method for modifying nickel microparticlesdescribed above.

Further, the present invention relates to a method for producing nickelmicroparticles, being a method for producing the nickel microparticlesusing a microreactor, the said microreactor comprising a firstprocessing surface and a second processing surface which are disposedfacing each other so as to be able to approach and/or separate from eachother, at least one of which rotates relative to the other, comprising astep of introducing at least two kinds of fluids to be processed betweenthe first processing surface and the second processing surface, a stepof generating a separating force which acts in a direction to separatethe first processing surface and the second processing surface from eachother by an introducing pressure of the at least two kinds of fluids tobe processed imparted to between the first processing surface and thesecond processing surface, a step of forming a thin film fluid by makingthe at least two kinds of fluids to be processed converge with eachother between the first processing surface and the second processingsurface kept at a minute distance and pass through between the firstprocessing surface and the second processing surface while keeping theminute distance between the first processing surface and the secondprocessing surface by the separating force, and a step of making thefluids to be processed react with each other in the thin film fluid andseparating nickel microparticles by the reaction.

Effects of the Invention

By using the modification method of the present invention, the rate andamount of weight loss in simultaneous TG-DTA measurement of nickelmicroparticles can be reduced, and the problem of a defect such ascracking in a burning process when, for example, a laminated ceramiccondenser is produced using slurry of nickel microparticles for aninternal electrode. Moreover, nickel microparticles modified by themodification method of the present invention are excellent in long-termstorage stability such as suppressing the formation of nickel hydroxide.Further, when the method for modifying nickel microparticles of thepresent invention is applied to nickel microparticles produced using amicroreactor which makes at least two kinds of fluids to be processedreact, a method for producing nickel microparticles comprising themethod for modifying nickel microparticles that thoroughly exhibits itsperformance and is low cost and capable of mass production can beprovided.

BRIEF DESCRIPTION OF DRAWINGS FIG. 1

This is a rough cross-section view of the fluid processing apparatusaccording to an embodiment of the present invention.

FIG. 2

This is a rough top view of the first processing surface of the fluidprocessing apparatus shown in FIG. 1.

FIG. 3

This is a SEM picture of the nickel microparticle powders obtained inComparative Example 1 of the present invention.

FIG. 4

This shows the results of a simultaneous TG-DTA measurement under anitrogen atmosphere of the nickel microparticles obtained in ComparativeExample 1 of the present invention.

FIG. 5

This shows the results of a simultaneous TG-DTA measurement under anitrogen atmosphere of the nickel microparticles obtained after acidprocessing in Example 1 of the present invention.

FIG. 6

This is a SEM picture of the nickel microparticles obtained by storingfor two weeks under an air atmosphere the nickel microparticle powdersobtained in Comparative Example 1 of the present invention.

FIG. 7

This shows the results of a simultaneous TG-DTA measurement under anitrogen atmosphere of nickel hydroxide.

FIG. 8

This is a TEM picture of the nickel microparticles obtained inComparative Example 1 of the present invention.

FIG. 9

This is a TEM picture of the nickel microparticles obtained after acidprocessing in Example 1 of the present invention.

FIG. 10

This is the XRD measurement results of the nickel microparticles inComparative Example 1 of the present invention.

FIG. 11

This is an enlarged view of the essential part of the XRD measurementresults of the nickel microparticles in Comparative Example 1 of thepresent invention.

FIG. 12

FIG. 12 (A) to FIG. 12 (G) are the XRD measurement results of the nickelmicroparticles obtained after acid processing and/or hydrogen peroxideprocessing in Examples 1, 2, 4, 8, 10, 17, and 24 of the presentinvention.

EMBODIMENTS FOR CARRYING OUT THE INVENTION

Hereunder, embodiments of the present invention will be explained indetail; but the present invention is not limited to only the followingembodiments.

In the present invention, the nickel microparticle is a microparticlemade mainly of nickel metal. A nickel microparticle hydroxylated oroxidized at least in part is also called a nickel microparticle. Inaddition, the nickel microparticle can also be one containing anelement(s) other than nickel to an extent not to affect the presentinvention. The nickel microparticle is not particularly restricted inparticle diameter or crystallite diameter. As the nickel microparticles,ones that are commonly commercially available may be purchased and themodification method of the present invention may be applied thereto, orthe modification method of the present invention may be applied tonickel microparticles separately prepared according to purpose.

In addition, nickel microparticles to which the modification method ofthe present invention is applicable can be any as long as weight lossthereof occurs due to heat treatment, and nickel microparticles producedby any method can be used such as ones prepared with a gas phase methodand ones prepared with a liquid phase method, but the effect isparticularly great when the nickel microparticles were prepared with aliquid phase method.

In the present invention, by making an acid and/or hydrogen peroxide acton the nickel microparticles mentioned above, the effect of reducing theweight loss rate in simultaneous TG-DTA measurement can be obtained.

Applicant of the presently applied invention presumes, as to bedescribed in detail hereinafter, that one of the reasons that nickelmicroparticles show weight loss is because nickel hydroxide is containedin part of the nickel microparticles.

FIG. 7 shows the results of a simultaneous TG-DTA measurement under anitrogen atmosphere of nickel hydroxide. The measurement range is 40° C.to 400° C. The TG curve shows a weight loss rate of about 19%, which isthe ratio (a theoretical value) of water contained in nickel hydroxide(Ni(OH)₂) from near 250° C., and in the entire measurement range, aweight loss rate of about 20%.

FIG. 4 shows the results of a simultaneous TG-DTA measurement ofconventional nickel microparticles, which are described in ComparativeExample 1 of the presently applied invention to be described later. Themeasurement range is 40° C. to 400° C. Also in these results, the TGcurve shows weight loss observed from near 250° C., and eventually showsa weight loss rate of about 1.25% in the entire measurement range, whichapproximates to the shape of the TG curve of nickel hydroxide mentionedabove. That is, the weight loss at near 250° C. or above indicates thepossibility that a reaction including dehydration from nickel hydroxidewas being effected, which is considered to lead to cracking and otherdefects in the burning process when a laminated ceramic condenser isproduced.

Given this, it is considered that the problem of cracking and the likethat occurs when, for example, producing a laminated ceramic condenserfor an electrode of which nickel microparticles are used can be solvedby reducing the weight loss in simultaneous TG-DTA measurement. It isdeduced that nickel microparticles a certain amount or more of weightloss of which occurs will further form nickel hydroxide during storageunder an air atmosphere.

The cause is not known exactly, but the inventor of the presentlyapplied invention has confirmed that nickel microparticles with whichthe weight loss rate in simultaneous TG-DTA measurement mentioned abovewas over 1.0% formed nickel hydroxide in only a few days and werefurther increased in the weight loss rate in a simultaneous TG-DTAmeasurement.

As a result of performing modifying processing of nickel microparticlesfor reducing the weight loss rate in a simultaneous TG-DTA measurementof nickel microparticles, particularly, the weight loss rate in 40° C.to 400° C. to 1.0% or less, as to be described in detail hereinafter,the inventor of the presently applied invention has found that nickelmicroparticles can be produced which, even when stored for a long periodof time, do not produce cracking and other defects in the burningprocess during production of a laminated ceramic condenser.

An illustrative example of the acid to be made to act on theabovementioned nickel microparticles includes inorganic acids such ashydrochloric acid, nitric acid, sulfuric acid, phosphoric acid, aquaregia, and mixed acid; and organic acids such as acetic acid and citricacid. A mixture of two or more kinds of acid may also be used. Althoughthe mechanism by which the weight loss in simultaneous TG-DTAmeasurement of the nickel microparticles can be reduced by making any ofthe abovementioned acids act is not clear, it is considered that thereduction is due to dissolution of nickel hydroxide, etc. present on thesurfaces of the particles or due to oxidation of nickel. Although thereason is not clear, the finding that by making an acid act on nickelmicroparticles, nickel hydroxide is not formed again and especially thatfurther formation of nickel hydroxide does not occur with nickelmicroparticles with which the weight loss rate in simultaneous TG-DTAmeasurement mentioned above is 1.0% or less, was surprising even to theinventor of the presently applied invention. Therefore, even among theabovementioned acids, an acid capable of dissolving nickel hydroxide oran acid capable of oxidizing nickel is preferable, and especially amongthese, an oxidizing acid or a mixture of acids that includes anoxidizing acid is preferable, and it is further preferable to use nitricacid or a mixture of acids that includes nitric acid. In this case, itis preferable to add the nickel microparticles to the solvent containingthe acid and to perform a stirring processing of a fixed time byultrasonic processing or by use of any of various stirrers or to performa microwave processing. The abovementioned acids also have the abilityto dissolve the nickel microparticles and therefore a molar ratio of anyof the abovementioned acids with respect to the nickel microparticles ispreferably within a range of 0.001 to 0.1 and even more preferablywithin a range of 0.005 to 0.05. If the molar ratio falls below 0.001,the possibility that the effects of the present invention will not beobtained becomes high, and if the molar ratio exceeds 0.1, a problemsuch as dissolution of the nickel microparticles may occur.

As the hydrogen peroxide to be made to act on the abovementioned nickelmicroparticles, a commonly commercially available hydrogen peroxidewater may be used. Although the mechanism by which the weight loss insimultaneous TG-DTA measurement of the nickel microparticles can bereduced by making the abovementioned hydrogen peroxide act is not clear,as in the case of making the acid act on the nickel microparticles, itis considered that the reduction is due to dissolution of nickelhydroxide, etc. present on the surfaces of the particles or due tooxidation of nickel or further due to oxidation of nickel hydroxide. Amolar ratio of the abovementioned hydrogen peroxide with respect to thenickel microparticles is preferably within a range of 0.001 to 2.0 andeven more preferably within a range of 0.001 to 1.0. Although incomparison to the abovementioned acid, the hydrogen peroxide is low inthe possibility of dissolving the nickel microparticles, in view of theeffect of reducing the weight loss, the molar ratio of the hydrogenperoxide with respect to the abovementioned nickel microparticles ispreferably 1.0 or less. The present invention may also be carried out byreplacing the hydrogen peroxide with ozone.

The processing of making any of the abovementioned acids act (acidprocessing) and the processing of making the hydrogen peroxide act(hydrogen peroxide processing) may be respectively carried out solely orboth may be carried out. As illustrated in an embodiment to be describedlater, the weight loss rate in the simultaneous TG-DTA measurement canbe reduced greatly by performing the hydrogen peroxide processing on thenickel microparticles on which the acid processing has been performed.Also, the same effect is provided by performing the acid processing onthe nickel microparticles on which the hydrogen peroxide processing hasbeen performed.

Preferably, the above-described acid processing and/or hydrogen peroxideprocessing are or is performed in any of various solvents. As examplesof such solvents, water (tap water, RO water, pure water, etc.) andorganic solvents (alcohol solvents, ketone solvents, ether solvents,aromatic solvents, carbon disulfide, aliphatic solvents, nitrilesolvents, sulfoxide solvents, halogen solvents, ester solvents, andionic solutions) can be cited. The present invention may be carried outby selecting one kind or a mixed solvent mixing two or more kinds fromamong such solvents according to purpose. In the present invention, inperforming the above-described acid processing and/or hydrogen peroxideprocessing, it is preferable to use a ketone solvent such as acetone,methyl ethyl ketone, and cyclohexanone, and especially preferable to useacetone as the at least one kind of solvent.

An example of an embodiment of the present invention is to perform theabove-described acid processing or hydrogen peroxide processing bypreparing a solution by mixing any of the abovementioned acids orhydrogen peroxide to any of the abovementioned solvents, adding thenickel microparticles into the solution, and performing the stirringprocessing by ultrasonic processing or by use of any of various stirrersor performing the microwave processing.

In the stirring processing in the modification method according to thepresent invention, a known stirrer or stirring means may be used andstirring energy may be controlled as appropriate. Details concerning thestirring energy are described in Japanese Patent Laid-Open PublicationNo. H04-114725 by Applicant of the presently applied invention.

The method for stirring in the present invention is not particularlyrestricted and may be carried out using a stirrer or dissolver,emulsifier, disperser, homogenizer, etc. of any of various shearingtypes, a friction type, a high-pressure jet type, an ultrasonic type,etc. For example, a continuous type emulsifier, such as Ultra-Turrax(manufactured by IKA Japan K.K.), Polytron (manufactured by KinematicaAG), TK Homomixer (manufactured by PRIMIX Corporation), Ebara Milder(manufactured by EBARA CORPORATION), TK Homomic Line Flow (manufacturedby PRIMIX Corporation), Colloid Mill (manufactured by Shinko Pantec Co.,Ltd.), Slasher (manufactured by NIPPON COKE & ENGINEERING CO., LTD.),Trigonal Wet Pulverizer (manufactured by Mitsui Miike ChemicalEngineering Machinery Co., Ltd.), Cavitron (manufactured by Eurotec,Ltd.), Fine Flow Mill (manufactured by Pacific Machinery & EngineeringCo., Ltd.), a batch-type emulsifier, such as Clearmix (manufactured byM. Technique Co., Ltd.), Clearmix Dissolver (manufactured by M.Technique Co., Ltd.), FILMIX (manufactured by PRIMIX Corporation), or acombination continuous/batch-type emulsifier can be cited. Also, thestirring processing is preferably performed using a stirrer providedwith a rotating stirring blade, especially the Clearmix (manufactured byM. Technique Co., Ltd.) or Clearmix Dissolver (manufactured by M.Technique Co., Ltd.) mentioned above.

An embodiment of applying the present invention to nickel microparticlesproduced using a microreactor shall now be described as an example.

Separation of Nickel Microparticle:

Firstly, a nickel-containing fluid, with which nickel metal or a nickelcompound is dissolved or dispersed in a solvent, and a reducing agentfluid, containing a reducing agent, are prepared. The nickel compound isnot particularly restricted, and an illustrative example thereofincludes inorganic salts of nickel such as a nitrate, sulfate, chloride,and hydroxide of nickel and hydrates of such inorganic salts; andorganic salts such as an acetate and acetylacetonate of nickel andorganic solvates of such organic salts. These may be used solely or aplurality may be used. The reducing agent is not particularly restrictedas long as it exhibits a property of reducing nickel ions, and anillustrative example thereof includes hydrides such as sodiumborohydride; hydrazines; and polyvalent alcohols such as ethyleneglycol. These may also be used solely or a plurality may be used bymixing or other method.

The abovementioned nickel-containing fluid and reducing agent fluid maybe used upon mixing, dissolving, or dispersing the abovementioned nickelmetal, nickel compound, or reducing agent in any of various solvents. Asthe abovementioned various solvents, the same solvents as the solventsused in the above-described acid processing and/or hydrogen peroxideprocessing may be used and a pH adjuster for adjusting the pH of thenickel-containing fluid and the reducing agent fluid may be added. Anillustrative example of the pH adjuster includes inorganic or organicacidic substances such as hydrochloric acid, sulfuric acid, nitric acid,aqua regia, trichloroacetic acid, trifluoroacetic acid, phosphoric acid,citric acid, and ascorbic acid; alkali hydroxides such as sodiumhydroxide and potassium hydroxide; basic substances such as aminesincluding triethylamine and dimethylamino ethanol; and salts of theseacidic substances and basic substances. These pH adjusters may be usedsolely or as a combination of two or more of them. Any of variousstirrers may be used to prepare the abovementioned nickel-containingfluid and reducing agent fluid. The abovementioned fluids that have beenprepared are mixed and the nickel component and the reducing agentcomponent in the fluids are made to react to separate the nickelmicroparticles. A case where a microreactor is used to mix theabovementioned fluids and separate the nickel microparticles shall beillustrated below.

In addition, as the microreactor, the one shown in FIG. 1, which is thesame as the apparatuses described in Patent Document 6 and PatentDocument 7, can be used. Hereunder, the microreactor will be describedin detail. In FIG. 1 and FIG. 2, reference character R indicates arotational direction.

The microreactor (hereinafter, referred to also as an apparatus) of thepresent embodiment is provided with two processing members of a firstprocessing member 10 and a second processing member 20 arranged oppositeto each other, wherein the first processing member 10 rotates. Thesurfaces arranged opposite to each other of the respective processingmembers 10 and 20 are made to be the respective processing surfaces. Thefirst processing member 10 is provided with a first processing surface 1and the second processing member 20 is provided with a second processingsurface 2.

Each of the processing surfaces 1 and 2 is connected to a flow path d1,d2 of the fluid to be processed and constitutes part of the flow path ofthe fluid to be processed. Distance between these processing surfaces 1and 2 is controlled so as to form a minute space usually in the range of1 mm or less, for example, 0.1 μm to 50 μm. With this, the fluid to beprocessed passing through between the processing surfaces 1 and 2becomes a forced thin film fluid forced by the processing surfaces 1 and2.

Moreover, this apparatus performs a fluid processing in which first andsecond fluids to be processed are reacted to separate nickelmicroparticles between the processing surfaces 1 and 2.

To more specifically explain, this apparatus is provided with a firstholder 11 for holding the first processing member 10, a second holder 21for holding the second processing member 20, a surface-approachingpressure imparting mechanism 43, a rotation drive mechanism (not shownin drawings), a first introduction part d1, a second introduction partd2, and fluid pressure imparting mechanisms p1 and p2. The fluidpressure imparting mechanisms p1 and p2 can be compressors or otherpumps.

In the abovementioned embodiment, the first processing member 10 and thesecond processing member 20 are disks with ring forms. Material of theprocessing members 10 and 20 is not only metal but also carbon,ceramics, sintered metal, abrasion-resistant steel, sapphire, and othermetal subjected to hardening treatment, and rigid material subjected tolining, coating, or plating. In the processing members 10 and 20 ofabovementioned embodiment, the first and the second surfaces 1 and 2arranged opposite to each other are mirror-polished, and arithmeticaverage roughness is 0.01 μm to 1.0 μm.

In the abovementioned embodiment, the second holder 21 is fixed to theapparatus, the first holder 11 attached to a rotary shaft 50 of therotation drive mechanism fixed to the same apparatus rotates, andthereby the first processing member 10 attached to this first holder 11rotates relative to the second processing member 20. As a matter ofcourse, the second processing member 20 may be made to rotate, or theboth may be made to rotate.

In the present invention, the rotation can be set to a speed of, forexample, 350 to 5000 rpm.

In the abovementioned embodiment, the second processing member 20approaches and separates from the first processing member 10 in thedirection of the rotary shaft 50, wherein a side of the secondprocessing member 20 opposite to the second processing surface 2 isaccepted in an accepting part 41 arranged in the second holder 21 so asto be able to rise and set. However, in contrast to the above, the firstprocessing member 10 may approach and separate from the secondprocessing member 20, or both the processing members 10 and 20 mayapproach and separate from each other.

The abovementioned accepting part 41 is a concave portion for acceptingthe side of the second processing member 20 opposite to the secondprocessing surface 2, and this concave portion is a groove being formedinto a ring. This accepting part 41 accepts the second processing member20 with sufficient clearance so that the side of the second processingmember 20 opposite to the second processing surface 2 may rise and set.

The surface-approaching pressure imparting mechanism is a mechanism togenerate force (hereinafter, surface-approaching pressure) to press thefirst processing surface 1 of the first processing member 10 and thesecond processing surface 2 of the second processing member 20 in thedirection to make them approach each other. The mechanism generates athin film fluid having minute thickness in a level of nanometer ormicrometer while keeping the distance between the processing surfaces 1and 2 in a predetermined minute distance by the balance between thesurface-approaching pressure and the force due to the fluid pressure toseparate the processing surfaces 1 and 2 from each other. In theabovementioned embodiment, the surface-approaching pressure impartingmechanism supplies the surface-approaching pressure by biasing thesecond processing member 20 toward the first processing member 10 by aspring 43 arranged in the second holder 21.

In addition, the first fluid to be processed which is pressurized withthe fluid pressure imparting mechanism p1 is introduced from the firstintroduction part d1 to the space inside the processing members 10 and20.

On the other hand, the second fluid to be processed which is pressurizedwith the fluid pressure imparting mechanism p2 is introduced from thesecond introduction part d2 via a path arranged inside the secondprocessing member 20 to the space inside the processing members 10 and20 through an opening d20 formed in the second processing surface.

At the opening d20, the first fluid to be processed and the second fluidto be processed converge and mix with each other.

At this time, the mixed fluid to be processed becomes a forced thin filmfluid by the processing surfaces 1 and 2 that keep the minute spacetherebetween, whereby the fluid is forced to move out from the circular,processing surfaces 1 and 2. The first processing member 10 is rotating;and thus, the mixed fluid to be processed does not move linearly frominside the circular, processing surfaces 1 and 2 to outside thereof, butdoes move spirally from the inside to the outside thereof by a resultantvector acting on the fluid to be processed, the vector being composed ofa moving vector toward the radius direction of the circle and a movingvector toward the circumferential direction.

Here, as shown in FIG. 2, in the first processing surface 1 of the firstprocessing member 10, a groove-like depression 13 extended toward anouter side from the central part of the first processing member 10,namely in a radius direction, may be formed. The depression 13 may be,as a plane view, curved or spirally extended on the first processingsurface 1, or, though not shown in the drawing, may be extended straightradially, or bent at a right angle, or jogged; and the concave portionmay be continuous, intermittent, or branched. In addition, thisdepression 13 may be formed also on the second processing surface 2, oron both the first and second processing surfaces 1 and 2. By forming thedepression 13 as mentioned above, the micro-pump effect can be obtainedso that the fluid to be processed may be sucked into between the firstand second processing surfaces 1 and 2.

It is preferable that the base edge of the depression 13 reach the innerperiphery of the first processing member 10. The front edge of thedepression 13 is extended to the direction of the outer periphery of thefirst processing surface 1; the depth thereof is made graduallyshallower (smaller) from the base edge to the front edge. Between thefront edge of the depression 13 and the outer peripheral of the firstprocessing surface 1 is formed a flat plane 16 not having the depression13.

The opening d20 described above is arranged preferably at a positionopposite to the flat surface of the first processing surface 1. Theopening d20 is arranged especially preferably at a position opposite tothe flat surface 16 located in the downstream of a position where thedirection of flow of the first fluid to be processed upon introductionby the micro-pump effect is changed to the direction of a spiral andlaminar flow formed between the processing surfaces. With this, mixingof a plurality of fluids to be processed and separation of themicroparticles therefrom can be effected under the condition of alaminar flow.

The second introduction part d2 preferably has directionality. Forexample, the direction of introduction from the opening d20 of thesecond processing surface 2 may be inclined at a predetermined elevationangle relative to the second processing surface 2, and introduction fromthe opening d20 of the second processing surface 2 may havedirectionality in a plane along the second processing surface 2, and thedirection of introduction of this second fluid may be in the outwarddirection departing from the center in a radial component of theprocessing surface and in the forward direction in a rotation componentof the fluid between the rotating processing surfaces. As mentionedabove, the flow of the first fluid to be processed at the opening d20 isa laminar flow and the second introduction part d2 has directionality,whereby the second fluid to be processed can be introduced between theprocessing surfaces 1 and 2 while suppressing the generation ofturbulence to the flow of the first fluid to be processed.

In addition, the fluid discharged to outside the processing members 10and 20 is collected via a vessel v into a beaker b as a dischargedsolution. In the embodiment of the present invention, the dischargedsolution contains nickel microparticles as to be described later.

Although, in the embodiment shown in FIG. 1, kinds of the fluid to beprocessed and numbers of the flow path thereof are set two respectively,they may be three or more. The opening for introduction arranged in eachprocessing member is not particularly restricted in its form, size, andnumber; and these may be changed as appropriate. For example, as shownin FIG. 1, shape of the opening d20 may be a concentric circular ringshape which encircles the central opening of the processing surface 2having a form of a ring-like disk, and the opening having the circularring shape may be any of continuous and discontinuous. The opening forintroduction may be arranged just before the first and second processingsurfaces 1 and 2 or in the side of further upstream thereof.

In the present invention, it is good enough only if the processing couldbe effected between the processing surfaces 1 and 2, and a methodwherein the second fluid to be processed is introduced from the firstintroduction part d1 and a solution containing the first fluid to beprocessed is introduced from the second introduction part d2 may also beused. For example, the expression “first” or “second” for each fluid hasa meaning for merely discriminating an n^(th) fluid among a plurality ofthe fluids present; and therefore, a third or more fluids can also existas in the foregoing.

By applying acid processing and/or hydrogen peroxide processing of thepresent invention to the nickel microparticles obtained using themicroreactor mentioned above, the uniform and homogeneous nickelmicroparticles can be provided with an effect of reducing the weightloss in simultaneous TG-DTA measurement, particularly, an effect ofreducing the weight loss that is observed from near 250° C., andlong-term storage stability such as suppressing the formation of nickelhydroxide.

As described above, the nickel microparticles are microparticles mademainly of nickel metal in the present invention. The nickelmicroparticles can be from any source. The modification method of thepresent invention may be applied to commonly commercially availablenickel microparticles, or the modification method of the presentinvention may be applied to nickel microparticles separately preparedaccording to purpose.

In addition, nickel microparticles to which the modification method ofthe present invention is applicable can be any as long as weight lossthereof occurs due to heat treatment, and can be produced by any method.The modification method of the present invention is applicable to allnickel microparticles weight loss of which occurs due to heat treatmentamong nickel microparticles that exist in the world, and the modifyingeffect is particularly great on nickel microparticles prepared with aliquid phase method.

Further, nickel microparticles modified by the modification method ofthe present invention do not require heat treatment.

Regarding these nickel microparticles, particularly, ones produced byseparating nickel microparticles using a liquid phase method, the nickelmicroparticles are preferably washed using a solvent such as pure waterand then dried, and it is preferable to apply the modification method ofthe present invention to washed and dried nickel microparticle powders,that is, to perform acid processing and/or hydrogen peroxide processingon washed and dried nickel microparticle powders.

On the surface of unwashed nickel microparticles, various substancesused for the separation reaction such as, for example, a reducing agentand its decomposed matter remain, and if acid processing and/or hydrogenperoxide processing is performed using the unwashed nickelmicroparticles, the substances may provide an adverse effect such thatthe amount of an acid and/or hydrogen peroxide to be used for the acidprocessing and/or hydrogen peroxide processing is increased.

EXAMPLES

Hereinafter, Examples and the like that specifically describe theconstitution and effect of the present invention will be exemplified;but the present invention is not limited only to these Examples.

Firstly, description will be given of a method of preparing anickel-containing fluid as solution A and a reducing agent fluid assolution B, mixing the solution A and the solution B using amicroreactor to separate nickel microparticles, and applying themodification method of the present invention to the obtained nickelmicroparticles for producing nickel microparticles.

ULREA SS-11 (manufactured by M. Technique Co., Ltd.) was used as themicroreactor. In this case, the solution A corresponds to a first fluidto be processed that is introduced from the first introduction part d1of the microreactor shown in FIG. 1, and the solution B corresponds to asecond fluid to be processed that is introduced from the secondintroduction part d2 of the same. The first introduction part d1 and thesecond introduction part d2 can be switched arbitrarily. Obtained nickelmicroparticles were analyzed under the following conditions.

XRD measurement was made by using the powder X-ray diffractionmeasurement instrument (product name: Empyrean, manufactured byPANalytical B. V.). The measurement conditions were as follows:measurement range of 10 to 1000, Cu anticathode, tube voltage of 45 kV,tube current of 40 mA, Bragg-Brentano HD (BBHD) used as an opticalsystem, and scanning speed of 9°/min. The crystallite diameter D wascalculated with use of the peak appeared near to 44° by using theScherrer's equation with reference to the silicon polycrystal plate.

D=K·λ/((β·cos θ)  Scherrer's equation:

Here, K is the Scherrer's constant provided as K=0.9, and λ is thewavelength of the X-ray tube used, β is the half-width, and θ is thediffraction angle.

TEM observation was made by using the transmission electron microscopeJEM-2100 (manufactured by JEOL Ltd.). The observation condition with theacceleration voltage of 200 kV was used.

SEM observation was made by using the scanning electron microscopeJFM-7500F (manufactured by JEOL Ltd.). The observation conditions withthe acceleration voltage of 5 kV and the magnification of 50,000 or morewere used. The average particle diameter was the average value of theparticle diameter measurements of 100 particles.

A simultaneous TG-DTA measurement was made using the simultaneoushigh-temperature differential scanning calorimetry/thermogravimetricanalyzer TG/DTA6300 (manufactured by Hitachi, Ltd.) was used. Themeasurement conditions were as follows: alumina used as a reference,rate of temperature increase of 5° C./min., measurement range of 40 to400° C. and measurement under a nitrogen atmosphere. A weight loss ratefrom 40° C., which is at the start of measurement, to 400° C. wasconfirmed. In addition, the weight of the sample was provided as 45 mg(±2 mg).

Separation of Nickel Microparticle:

Solution A was prepared by mixing and dissolving each of the nickelsulfate hexahydrate/concentrated sulfuric acid/ethylene glycol/purewater (weight ratio of 2.33/0.86/83.54/13.27) by stirring for 60 minuteswith a rotation number of 20000 rpm and a processing temperature of 24to 60° C. using a high-speed emulsification/dispersion apparatus Cleamix(product name: CLM-2.2S, manufactured by M. Technique Co., Ltd.).Solution B was prepared by mixing and dissolving each of the hydrazinemonohydrate/sodium hydroxide/pure water (weight ratio of 70/5/25) bystirring for 30 minutes with a rotation number of 20000 rpm and aprocessing temperature of 25° C. using the same high-speedemulsification/dispersion apparatus Cleamix (product name: CLM-2.2S,manufactured by M. Technique Co., Ltd.).

The solution A was introduced at 165° C. and 600 ml/min. from the firstintroduction part d1 of the microreactor shown in FIG. 1 between theprocessing surfaces 1 and 2, and while the processing member 10 wasrotated at 1700 rpm, the solution B was introduced at 60° C. and 65ml/min. from the second introduction part d2 between the processingsurfaces 1 and 2, whereby the solution A and the solution B were mixedbetween the processing surfaces 1 and 2 to separate nickelmicroparticles. A slurry liquid containing the nickel microparticlesseparated between the processing surfaces 1 and 2 was discharged frombetween the processing surfaces 1 and 2, and collected via the vessel vinto the beaker b.

Washing of Nickel Microparticle

The discharged solution collected into the beaker b was allowed to standuntil it was cooled to 60° C. or less, and the nickel microparticleswere settled. The PH of the discharged solution was 8.45 (measurementtemperature: 42.5° C.). The supernatant solution in the beaker b wasremoved, and pure water 20 to 1500 times the weight of the settlednickel microparticles was added, and stirred for five minutes with arotation number of 6000 rpm and a processing temperature of 25° C. usingCleamix 2.2S to wash the nickel microparticles. The washing operationwas repeated for 3 times, and then the nickel microparticles were againsettled, and the supernatant solution was removed to obtain an aqueouswet cake (1) of nickel microparticles.

Drying of Nickel Microparticle

The aqueous wet cake (1) of nickel microparticles was dried at −0.10MpaG and 20° C. for 15 hours or more to obtain nickel microparticlepowders. The content of water in the nickel microparticle powders was 89μg/g. It is preferable to dry the nickel microparticle powders until thecontent of water therein becomes 1000 μg/g or less, preferably, 500 μg/gor less, and more preferably, 100 μg/g or less. A SEM picture of thenickel microparticle powders after drying is shown in FIG. 3 asComparative Example 1 of the presently applied invention, and XRDmeasurement results thereof, in FIG. 10(A), and an enlarged view of theessential part of the XRD measurement results thereof, in FIG. 11(spectrum (A)). From the SEM observation results, the average particlediameter of the nickel microparticles was 86.4 nm, and from the XRDmeasurement results, the crystallite diameter was 41.5 nm. In addition,a dispersion solution obtained by dispersing the nickel microparticlepowders after drying in acetone was allowed to drip onto a collodionfilm to obtain a TEM observation sample. A TEM picture is shown in FIG.8. As shown in FIG. 8, a thin membranous substance was observed on thesurface of the nickel microparticles. Moreover, in the XRD measurementresults (FIG. 11), peaks derived from nickel hydroxide were detectedbesides peaks derived from nickel, and it was confirmed that 3.4% byweight of nickel hydroxide was contained in the nickel powder. In FIG.11, the peaks with filled circles are the peaks of nickel hydroxide.Further, results of a simultaneous TG-DTA measurement of the nickelmicroparticle powders after drying are shown in FIG. 4. Weight loss of1.256% was confirmed in the measurement range mentioned above.

Temporal Change of Nickel Microparticle

A SEM picture of nickel microparticles after the nickel microparticlepowders of Comparative Example 1 mentioned above were stored for twoweeks under an air atmosphere is shown in FIG. 6, and XRD measurementresults thereof, in FIG. 10(B), and an enlarged view of the essentialpart of the XRD measurement results thereof, in FIG. 11 (spectrum (B)).As can be understood by comparing with FIG. 3, in FIG. 6, a substancethat seemed to have separated due to a temporal change was observedbetween the nickel microparticles.

In addition, it was understood in the XRD measurement results afterstoring for two weeks under an air atmosphere (FIG. 10(B), FIG. 11) thatnickel hydroxide was increased to 16.2% by weight due to a temporalchange during the storage. Moreover, in the measurement range, theweight loss rate in the simultaneous TG-DTA measurement showed anincrease to 1.692%. It is deduced from the above that, as a result ofstoring for two weeks under an air atmosphere, part of the nickelmicroparticles have changed to nickel hydroxide and the weight loss ratehas increased due to the change.

Example 1: Acid Processing

0.15 g of the nickel microparticle powders of Comparative Example 1mentioned above was charged into 14.85 g of a solution obtained bymixing nitric acid/water/acetone at a weight ratio of 0.005/0.003/99.992and subjected to a stirring processing for 15 minutes with a processingtemperature of 20° C. by a ultrasonic disperser (UP200S, manufactured byHielscher Ultrasonics GmbH) to thereby perform acid processing on thenickel microparticles. After the acid processing, the nickelmicroparticles in the solution were settled, the supernatant solutionwas removed, and pure water 20 to 1500 times the weight of the nickelmicroparticles was added and washed the nickel microparticles by theultrasonic cleaner described above. The washing operation was repeatedfor 3 times, and an aqueous wet cake (2) of nickel microparticlesobtained after the washing was prepared, and then, the aqueous wet cake(2) was dried at −0.10 MpaG and 20° C. for 15 hours or more to obtainnickel microparticle powders. The content of water in the nickelmicroparticle powders was 36 μg/g. It is preferable to dry the nickelmicroparticle powders until the content of water therein becomes 1000μg/g or less, preferably, 500 μg/g or less, and more preferably, 100μg/g or less.

Effect of Example 1

A dispersion solution obtained by dispersing the nickel microparticlepowders obtained by the acid processing in acetone was allowed to driponto a collodion film to obtain a TEM observation sample. A TEM pictureis shown in FIG. 9. Unlike the TEM picture before the acid processing,that is, the TEM picture (FIG. 8) of the nickel microparticles obtainedin Comparative Example 1, no thin membranous substance was observed onthe surface of the nickel microparticles. The thin membranous substanceon the surface of nickel microparticles is a hydroxide of nickel, andconsidered to be the thin membranous substance dissolved by the acidprocessing. Results of a simultaneous TG-DTA measurement of the nickelmicroparticle powders after the acid processing are shown in FIG. 5. Theweight loss rate was 0.793%. By thus subjecting nickel microparticles toacid processing by an acetone solution containing nitric acid, theweight loss rate in the simultaneous TG-DTA measurement could be reducedas compared with Comparative Example 1. In addition, XRD measurementresults of the nickel microparticle powders obtained in Example 1 areshown in FIG. 12(A). As shown in FIG. 12(A), no peaks derived fromnickel hydroxide were detected.

As a result of a simultaneous TG-DTA measurement performed again afterstoring the nickel microparticle powders for two weeks under an airatmosphere, the weight loss rate in the measurement range mentionedabove showed a further reduction to 0.643%. It was understood that thenickel microparticles (Comparative Example 1) without having beensubjected to the acid processing of the present invention showed anincrease in the weight loss rate in the simultaneous TG-DTA measurementdue to storage for two weeks under an air atmosphere, whereas the nickelmicroparticles (Example 1) with having been subjected to the acidprocessing of the present invention, even when stored under an airatmosphere, provides an effect of reducing the weight loss rate frombefore the storage.

With the nickel microparticles applied with the acid processing ofExample 1, even when this was stored for a month under an airatmosphere, no such substance that seemed to have separated as observedin the SEM picture of FIG. 6 described above was confirmed, and therewas also no change in XRD measurement results from those immediatelyafter the acid processing, and no peaks derived from nickel hydroxidewere detected. It was understood by this that applying the acidprocessing of the present invention to nickel microparticles can reducethe weight loss rate in simultaneous TG-DTA measurement, and further cansuppress the formation of nickel hydroxide during long-term storage.

Example 2: Processing of Making Acid Act on Nickel Microparticles UsingStirrer Provided with Rotating Stirring Blade

15 g of the nickel microparticle powders of Comparative Example 1mentioned above was charged into 1485 g of a solution obtained by mixingnitric acid/water/acetone at a weight ratio of 0.005/0.003/99.992 andstirred for 15 minutes with a processing temperature of 20° C. by ahigh-speed emulsification/dispersion apparatus Cleamix (product name:CLM-2.2S, manufactured by M. Technique Co., Ltd.) to thereby performacid processing on the nickel microparticles. After the acid processing,the nickel microparticles in the solution were settled, the supernatantsolution was removed, and pure water 20 to 700 times the weight of thenickel microparticles was added and washed the nickel microparticlesusing Cleamix. The washing operation was repeated for 3 times, and anaqueous wet cake (3) of nickel microparticles obtained after the washingwas prepared, and then, the aqueous wet cake (3) was dried at −0.10 MpaGand 20° C. for 15 hours or more to obtain nickel microparticle powders.

Effect of Example 2

From the results of a simultaneous TG-DTA measurement after the acidprocessing, the weight loss rate was 0.644%, and the weight loss rate inthe simultaneous TG-DTA measurement could be reduced as compared withComparative Example 1. In addition, XRD measurement results of thenickel microparticle powders obtained in Example 2 are shown in FIG.12(C). As shown in FIG. 12(C), no peaks derived from nickel hydroxidewere detected. As a result of a simultaneous TG-DTA measurementperformed again after storing the nickel microparticles for two weeksunder an air atmosphere, the weight loss rate in the measurement rangementioned above showed a reduction to 0.533%. This way, performing acidprocessing using a stirrer provided with a rotating stirring bladeproves to be further effective for a reduction in weight loss.

In addition, other examples of acid processing; Example 3 to Example 7and Example 16 to Example 19, which were changed in the method forseparating nickel microparticles or in the molar ratio of an acid tonickel microparticles when acid processing was performed will bedescribed later. The molar ratio of an acid to nickel microparticleswhen acid processing was performed was changed by adjusting the weightratio of nitric acid/water/acetone in the solution (ultrasonicdisperser: 14.85 g, stirrer: 1485 g) to be used for the acid processingrelative to the nickel microparticle powders (ultrasonic disperser: 0.15g, stirrer: 15 g) to be subjected to the acid processing.

Example 8: Hydrogen Peroxide Processing

Explanation will be made as to a processing (hydrogen peroxideprocessing) for which an acid was changed to hydrogen peroxide in theprocessing of making an acid act on nickel microparticles of Example 1.0.15 g of the nickel microparticles of Comparative Example 1 mentionedabove was charged into 14.85 g of a solution obtained by mixing hydrogenperoxide/water/acetone at a weight ratio of 0.005/0.012/99.983 andstirred for 15 minutes with a processing temperature of 20° C. by aultrasonic disperser (UP200S, manufactured by Hielscher UltrasonicsGmbH) to thereby perform a processing of making hydrogen peroxide act onthe nickel microparticles. In the same manner as with the case of acidprocessing, after the hydrogen peroxide processing, the nickelmicroparticles in the solution were settled, the supernatant solutionwas removed, and pure water 20 to 1500 times the weight of the nickelmicroparticles was added and washed the nickel microparticles by theultrasonic cleaner described above. The washing operation was repeatedfor 3 times, and an aqueous wet cake (4) of nickel microparticlesobtained after the washing was prepared, and then, the aqueous wet cake(4) of nickel microparticles was dried at −0.10 MpaG and 20° C. for 15hours or more to obtain nickel microparticle powders. Similar to thecase of acid processing, the content of water in the nickelmicroparticle powders was 42 μg/g. It is preferable to dry the nickelmicroparticle powders until the content of water therein becomes 1000μg/g or less, preferably, 500 μg/g or less, and more preferably, 100μg/g or less.

Effect of Example 8

As a result of TEM observation of the nickel microparticle powdersobtained in Example 8 made by the same method as in Comparative Example1, the thin membranous substance observed on the surface of the nickelmicroparticles obtained in Comparative Example 1 was not observed. Fromthe results of a simultaneous TG-DTA measurement of the nickelmicroparticle powders after the hydrogen peroxide processing, the weightloss rate in the measurement range was 0.989%. By thus subjecting nickelmicroparticles to hydrogen peroxide processing by an acetone solutioncontaining hydrogen peroxide, the weight loss rate in the simultaneousTG-DTA measurement could be reduced as compared with ComparativeExample 1. In addition, XRD measurement results of the nickelmicroparticle powders obtained in Example 8 are shown in FIG. 12(B). Asshown in FIG. 12(B), no peaks derived from nickel hydroxide weredetected. As a result of a simultaneous TG-DTA measurement performedagain after storing the nickel microparticle powders for two weeks underan air atmosphere, the weight loss rate in the measurement rangementioned above showed a further reduction to 0.741%. It was understoodthat the nickel microparticles (Comparative Example 1) without havingbeen subjected to the hydrogen peroxide processing of the presentinvention showed an increase in the weight loss rate in the simultaneousTG-DTA measurement due to storage for two weeks under an air atmosphere,whereas the nickel microparticles (Example 8) with having been subjectedto the hydrogen peroxide processing of the present invention, even whenstored under an air atmosphere, provides an effect of reducing theweight loss rate from before the storage.

Similar to the nickel microparticles for which the acid processing ofExample 1 was carried out, also with the nickel microparticles for whichthe hydrogen peroxide processing of Example 8 was carried out, even whenthis was stored for a month under an air atmosphere, no such substancethat seemed to have separated as observed in the SEM picture of FIG. 6mentioned above was confirmed, and there was also no change in XRDmeasurement results from those immediately after the hydrogen peroxideprocessing, and no peaks derived from nickel hydroxide were detected. Itwas understood by this that applying the hydrogen peroxide processing ofthe present invention to nickel microparticles can reduce the weightloss rate and amount in simultaneous TG-DTA measurement, and further cansuppress the formation of nickel hydroxide during long-term storage. Inaddition, other examples changed in the method for separating nickelmicroparticles or in the molar ratio of hydrogen peroxide to nickelmicroparticles when hydrogen peroxide processing was performed; Example9 to Example 14 and Example 20 to Example 23 will be described later.The molar ratio of hydrogen peroxide to nickel microparticles whenhydrogen peroxide processing was performed was changed by adjusting theweight ratio of hydrogen peroxide/water/acetone in the solution(ultrasonic disperser: 14.85 g, stirrer: 1485 g) to be used for thehydrogen peroxide processing relative to the nickel microparticlepowders (ultrasonic disperser: 0.15 g, stirrer: 15 g) to be subjected tothe hydrogen peroxide processing.

Example 15: Processing of Making Both of Acid and Hydrogen Peroxide Acton Nickel Microparticles

Explanation will be made as to Example 15 in which both of the acidprocessing and hydrogen peroxide processing mentioned above were appliedto nickel microparticles.

0.15 g of the nickel microparticle powders of Comparative Example 1mentioned above was charged into 14.85 g of a solution obtained bymixing nitric acid/water/acetone at a weight ratio of 0.010/0.007/99.983and stirred for 15 minutes with a processing temperature of 20° C. by aultrasonic disperser (UP200S, manufactured by Hielscher UltrasonicsGmbH) to thereby perform acid processing on the nickel microparticles.

After the acid processing, the nickel microparticles contained in thesolution were settled, the supernatant solution was removed, and purewater 20 to 1500 times the weight of the nickel microparticles was addedand the nickel microparticles were washed by the ultrasonic cleanerdescribed above. The washing operation was repeated for 3 times, and anaqueous wet cake (5) of nickel microparticles obtained after the washingwas prepared, and then, the aqueous wet cake (5) was dried at −0.10 MpaGand 20° C. for 15 hours or more to obtain nickel microparticle powders.

0.15 g of the obtained nickel microparticle powders was charged into14.85 g of a solution obtained by mixing hydrogen peroxide/water/acetoneat a weight ratio of 0.010/0.023/99.967 and stirred for 15 minutes witha processing temperature of 20° C. by the ultrasonic disperser describedabove to thereby perform hydrogen peroxide processing on the nickelmicroparticles.

After the hydrogen peroxide processing, the nickel microparticlescontained in the solution were settled, the supernatant solution wasremoved, and pure water 20 to 1500 times the weight of the nickelmicroparticles was added and washed the nickel microparticles by theultrasonic cleaner. The washing operation was repeated for 3 times, andan aqueous wet cake (6) of nickel microparticles obtained after thewashing was prepared, and then, the aqueous wet cake (6) was dried at−0.10 MpaG and 20° C. for 15 hours or more to obtain nickelmicroparticle powders.

Effect of Example 15

From the results of a simultaneous TG-DTA measurement after the hydrogenperoxide processing of the nickel microparticle powders, the weight lossin the measurement range mentioned above was 0.598%. By performing bothof the acid processing and hydrogen peroxide processing mentioned above,the weight loss rate in the simultaneous TG-DTA measurement could befurther reduced as compared with the case (Example 3, Example 10) whereacid processing or hydrogen peroxide processing was carried out solely.In addition, from XRD measurement results of the nickel microparticlepowders obtained in Example 15, no peaks derived from nickel hydroxidewere detected. Moreover, also with the nickel microparticles for whichboth of the acid processing and hydrogen peroxide processing werecarried out, even when this was stored for a month under an airatmosphere, no such substance that seemed to have separated as observedin the SEM picture of FIG. 6 mentioned above was confirmed, and also inXRD measurement results, no peaks derived from nickel hydroxide weredetected. It is understood by this that applying both the acidprocessing and hydrogen peroxide processing to nickel microparticles canreduce the weight loss amount in simultaneous TG-DTA measurement, andfurther can suppress the formation of nickel hydroxide during long-termstorage.

As a result of a simultaneous TG-DTA measurement performed again afterstoring the nickel microparticle powders for two weeks under an airatmosphere, the weight loss rate in the measurement range mentionedabove showed a reduction to 0.492%. It was understood that the nickelmicroparticles of Comparative Example 1 showed an increase in the weightloss rate in the simultaneous TG-DTA measurement due to storage for twoweeks under an air atmosphere, whereas the nickel microparticles withhaving been subjected to both of the acid processing and hydrogenperoxide processing of the present invention, by being stored under anair atmosphere, provides an effect of reducing the weight loss rate frombefore the storage. It was understood by this that applying both theacid processing and hydrogen peroxide processing of the presentinvention to nickel microparticles can reduce the weight loss rate andamount in simultaneous TG-DTA measurement, and further can suppress theformation of nickel hydroxide during long-term storage. In addition,Example 24 changed in the method for separating nickel microparticleswill be described later.

Another Example Using Microreactor

Processing conditions and results of the acid processing or hydrogenperoxide processing mentioned above for nickel microparticles producedwith the molar ratio of nitric acid or hydrogen peroxide to nickelmicroparticles changed when the acid processing or hydrogen peroxideprocessing was performed are shown in the following Table 1 togetherwith Examples 1, 2, 8, and 15. In addition, operation procedures thatare not described are the same as the above. Moreover, the molar ratioof an acid to nickel microparticles when acid processing was performedwas changed by adjusting the weight ratio of nitric acid/water/acetonein the solution (ultrasonic disperser: 14.85 g, stirrer: 1485 g) to beused for the acid processing relative to the nickel microparticlepowders (ultrasonic disperser: 0.15 g, stirrer: 15 g) to be subjected tothe acid processing, and the molar ratio of hydrogen peroxide to nickelmicroparticles when hydrogen peroxide processing was performed waschanged by adjusting the weight ratio of hydrogen peroxide/water/acetonein the solution (ultrasonic disperser: 14.85 g, stirrer: 1485 g) to beused for the hydrogen peroxide processing relative to the nickelmicroparticle powders (ultrasonic disperser: 0.15 g, stirrer: 15 g) tobe subjected to the hydrogen peroxide processing.

TABLE 1 Weight loss rate Processing Molar ratio of acid or (%) fromApparatus used temperature Processing time hydrogen peroxide tomeasurement start Crystallite for processing (° C.) (min.) nickelmicroparticles to 400° C. diameter (nm) Comparative Unprocessed — — — —1.256 41.5 Example 1 Example 1 (1) Acid Ultrasonic 20 15 0.005 0.79341.3 processing disperser (UP200S) Example 2 Stirrer 20 15 0.005 0.64442.8 (Cleamix) Example 3 Ultrasonic 20 15 0.009 0.791 42.4 disperser(UP200S) Example 4 Ultrasonic 20 15 0.012 0.762 43.1 disperser (UP200S)Example 5 Ultrasonic 20 15 0.019 0.785 41.9 disperser (UP200S) Example 6Ultrasonic 20 15 0.037 0.813 41.5 disperser (UP200S) Example 7Ultrasonic 20 15 0.093 0.794 41.3 disperser (UP200S) Example 8 (2)Hydrogen Ultrasonic 20 15 0.009 0.989 41.1 peroxide disperser processing(UP200S) Example 9 Ultrasonic 20 15 0.014 0.782 41.0 disperser (UP200S)Example 10 Ultrasonic 20 15 0.017 0.644 42.8 disperser (UP200S) Example11 Ultrasonic 20 15 0.022 0.894 42.7 disperser (UP200S) Example 12Ultrasonic 20 15 0.173 0.753 42.6 disperser (UP200S) Example 13Ultrasonic 20 15 0.863 0.821 41.8 disperser (UP200S) Example 14Ultrasonic 20 15 1.725 0.920 41.6 disperser (UP200S) Example 15 (1) +(2) Ultrasonic 20 15 HNO₃: 0.009 0.598 43.2 disperser H₂O₂: 0.017(UP200S)

It can be understood from Table 1 that the weight loss rate insimultaneous TG-DTA measurement reduces as a result of the acidprocessing and/or hydrogen peroxide processing being applied.

Also, XRD measurement results of the nickel microparticle powdersobtained in Example 4 are shown in FIG. 12(D), and XRD measurementresults of the nickel microparticle powders obtained in Example 10 areshown in FIG. 12(E). In either example, no peaks derived from nickelhydroxide were detected in the XRD measurement results, and even afterstorage for a month under an air atmosphere, no such substance thatseemed to have separated as observed in the SEM picture of FIG. 6 wasconfirmed, and no peaks derived from nickel hydroxide were detected inthe XRD measurement results.

Further, according to Table 1, all examples resulted in crystallitediameters that have no problem with the application to a laminatedceramic condenser or the like.

Example by Batch Method

Next, as a batch method, the same solutions as those in ComparativeExample 1 were used as solution A and solution B and the acid processingand/or hydrogen peroxide processing of the present invention was appliedto nickel microparticles separated in a beaker. Processing conditionsand results of the acid processing and/or hydrogen peroxide processingare shown in Table 2.

In the abovementioned batch method, with 600 ml of the solution A beingstirred at 100° C. in a beaker and at 150 rpm using a magnetic stirrer,65 ml of the solution B was charged in a minute at 90° C., and thenstirred for 60 minutes at 100° C. and 150 rpm using a magnetic stirrerto separate nickel microparticles. Thereafter, in the same manner aswith Comparative Example 1, washing and drying were performed, and theobtained nickel microparticle powders were used as Comparative Example2, and for the nickel microparticles obtained in Comparative Example 2,acid processing and/or hydrogen peroxide processing was carried outusing a ultrasonic disperser (UP200S, manufactured by HielscherUltrasonics GmbH) or a high-speed emulsification/dispersion apparatusCleamix (product name: CLM-2.2S, manufactured by M. Technique Co.,Ltd.). In addition, processing conditions that are not included in thetable are the same as those of Examples 1 to 15. From SEM observationresults, the average particle diameter of nickel microparticles ofComparative Example 2 was 116 nm, and from XRD measurement results, thecrystallite diameter of Comparative Example 2 was 14.1 nm.

TABLE 2 Weight loss rate Processing Molar ratio of acid or (%) fromApparatus used temperature Processing time hydrogen peroxide tomeasurement start Crystallite for processing (° C.) (min.) nickelmicroparticles to 400° C. diameter (nm) Comparative Unprocessed — — — —1.701 14.1 Example 2 Example 16 (1) Acid Ultrasonic 20 15 0.005 0.97914.3 processing disperser (UP200S) Example 17 Stirrer 20 15 0.009 0.85915.1 Example 18 (Cleamix) 20 15 0.037 0.989 14.9 Example 19 20 15 0.0930.899 14.9 Example 20 (2) Hydrogen Ultrasonic 20 15 0.009 0.919 14.2peroxide disperser processing (UP200S) Example 21 Stirrer 20 15 0.0170.949 15.2 Example 22 (Cleamix) 20 15 0.173 0.863 15.2 Example 23Ultrasonic 20 15 1.725 0.894 14.6 disperser (UP200S) Example 24 (1) +(2) Ultrasonic 20 15 HNO₃: 0.009 0.687 15.6 disperser H₂O₂: 0.017(UP200S)

It can be understood from Table 2 that, similar to the case of nickelmicroparticles (Comparative Example 1) produced using a microreactor,also with the nickel microparticles (Comparative Example 2) produced bya batch method, the weight loss rate in a simultaneous TG-DTAmeasurement reduces as a result of the acid processing and/or hydrogenperoxide processing being applied.

Also, XRD measurement results of the nickel microparticle powdersobtained in Example 17 are shown in FIG. 12(F), and XRD measurementresults of the nickel microparticle powders obtained in Example 24 areshown in FIG. 12(G). In either example, no peaks derived from nickelhydroxide were detected in the XRD measurement results, and even afterstorage for a month under an air atmosphere, no such substance thatseemed to have separated as observed in the SEM picture of FIG. 6 wasconfirmed, and no peaks derived from nickel hydroxide were detected inthe XRD measurement results.

Further, according to Table 2, all examples resulted in crystallitediameters that have no problem with the application to a laminatedceramic condenser or the like.

It was understood from the above results that applying the acidprocessing and/or hydrogen peroxide processing of the present inventionto nickel microparticles can reduce the weight loss rate in simultaneousTG-DTA measurement, and further can suppress the formation of nickelhydroxide during long-term storage.

REFERENCE SIGNS LIST

-   1 first processing surface-   2 second processing surface-   10 first processing member-   11 first holder-   20 second processing member-   21 second holder-   d1 first introduction part-   d2 second introduction part-   d20 opening

1. A method for modifying nickel microparticles comprising a step ofmaking an acid and/or hydrogen peroxide act on nickel microparticlesweight loss of which occurs due to heat treatment such as burning. 2.The method for modifying nickel microparticles according to claim 1,wherein the step of making an acid and/or hydrogen peroxide act reducesa rate of weight loss due to heat treatment of the nickelmicroparticles.
 3. The method for modifying nickel microparticlesaccording to claim 2, wherein the rate of weight loss due to heattreatment of the nickel microparticles is a weight loss rate insimultaneous thermogravimetry-differential thermal analysis measurement,and the weight loss rate in a simultaneous thermogravimetry-differentialthermal analysis measurement under a nitrogen atmosphere of the nickelmicroparticles is 1% or less in a range of 40° C. to 400° C.
 4. Themethod for modifying nickel microparticles according to claim 1, whereinnitric acid or a mixture of acids that include nitric acid is used asthe acid.
 5. The method for modifying nickel microparticles according toclaim 1, wherein the nickel microparticles and acid and/or hydrogenperoxide are made to act in a ketonic solvent.
 6. The method formodifying nickel microparticles according to claim 1, wherein a molarratio of the acid to the nickel microparticles is in a range of 0.001 to0.1.
 7. The method for modifying nickel microparticles according toclaim 1, wherein a molar ratio of the hydrogen peroxide to the nickelmicroparticles is in a range of 0.001 to 2.0.
 8. The method formodifying nickel microparticles according to claim 1, wherein the stepof making an acid and/or hydrogen peroxide act includes an ultrasonicprocessing, a stirring processing, or a microwave processing.
 9. Themethod for modifying nickel microparticles according to claim 8, whereinthe stirring processing is performed using a stirrer provided with arotating stirring blade.
 10. The method for modifying nickelmicroparticles according to claim 1, wherein powder of the nickelmicroparticles on which the acid and/or hydrogen peroxide was made toact is stored under an air atmosphere.
 11. The method for modifyingnickel microparticles according to claim 1, wherein the nickelmicroparticles are nickel microparticles separated by a microreactorwhich makes at least two kinds of fluids to be processed react.
 12. Amethod for modifying nickel microparticles comprising a step of making asubstance which reacts with nickel hydroxide act on nickelmicroparticles on at least surfaces of which nickel hydroxide is presentto reduce the nickel hydroxide.
 13. A method for producing nickelmicroparticles comprising the modification method according to claim 1.14. The method for producing nickel microparticles according to claim13, being a method for producing the nickel microparticles using amicroreactor, the said microreactor comprising: a first processingsurface and a second processing surface which are disposed facing eachother so as to be able to approach and/or separate from each other, atleast one of which rotates relative to the other, comprising: a step ofintroducing at least two kinds of fluids to be processed between thefirst processing surface and the second processing surface; a step ofgenerating a separating force which acts in a direction to separate thefirst processing surface and the second processing surface from eachother by an introducing pressure of the at least two kinds of fluids tobe processed imparted to between the first processing surface and thesecond processing surface; a step of forming a thin film fluid by makingthe at least two kinds of fluids to be processed converge with eachother between the first processing surface and the second processingsurface kept at a minute distance and pass through between the firstprocessing surface and the second processing surface while keeping theminute distance between the first processing surface and the secondprocessing surface by the separating force; and a step of making thefluids to be processed react with each other in the thin film fluid andseparating nickel microparticles by the reaction.
 15. The method formodifying nickel microparticles according to claim 2, wherein nitricacid or a mixture of acids that include nitric acid is used as the acid.16. The method for modifying nickel microparticles according to claim 3,wherein nitric acid or a mixture of acids that include nitric acid isused as the acid.
 17. The method for modifying nickel microparticlesaccording to claim 2, wherein the nickel microparticles and acid and/orhydrogen peroxide are made to act in a ketonic solvent.
 18. The methodfor modifying nickel microparticles according to claim 3, wherein thenickel microparticles and acid and/or hydrogen peroxide are made to actin a ketonic solvent.
 19. The method for modifying nickel microparticlesaccording to claim 4, wherein the nickel microparticles and acid and/orhydrogen peroxide are made to act in a ketonic solvent.
 20. The methodfor modifying nickel microparticles according to claim 2, wherein amolar ratio of the acid to the nickel microparticles is in a range of0.001 to 0.1.